Hand held computing devices, such as personal digital assistants (“PDAs”) and radiotelephones (collectively referred to as “hand held devices”), have widely adopted touch sensitive screen panels (“touch screens”), overlaid on a display screen, such as a liquid crystal display (“LCD”). A touch screen serves as a data/command input mechanism so that, when a user employs a stylus to touch a touch screen at a selected location, the position of the selected location, alone or relative to the display screen, is identified and processed by a signal processor or its equivalent circuit(s) resident on the hand held device.
A conventional hand held device automatically activates an associated touch screen upon power-up, with the touch screen remaining activated until an explicit power-down. Alternatively, the device deactivates the touch screen by measuring accumulated idle time (usually measured in minutes) since the touch screen was last touched, using a time-out mechanism. Reactivating a touch screen from a deactivated state is performed by pressing one or more keys, such as a power key or other designated key. Some radiotelephones that are equipped with touch screens also activate or deactivate an associated touch screen through flip of a keypad hinged on the device housing so that the touch screen (1) is in an activated mode when the keypad is opened and (2) is in a deactivated mode when the keypad is closed. A conventional hand held device with only a time-out mechanism does not provide adequate protection from accidental activation of the associated touch screen before time-out occurs, through accidental pressing or touching of an activation mechanism while the device is carried in the user's pocket, pocketbook, briefcase or similar container. A time-out mechanism consumes additional battery power, when the device is not in use. Although a hand held device with a flip keypad or a protective cover can prevent accidental activation and can provide some power conservation, a hand held device without a flip keypad or a protective cover cannot.
What is needed is a automatic activation and deactivation mechanism for a touch screen that prevents accidental activation of touch screen components and that conserves battery power by monitoring more closely the present state of the hand held device. Preferably, the activation and deactivation mechanism should be flexible enough to rely on one or on a plurality of state monitoring approaches.